The invention generally relates to a technique and system to process a seismic signal to determine an attribute of a geological layer.
A seismic survey typically is employed for purposes of discovering hydrocarbon (oil and gas) deposits in geological formations. In the seismic survey, sources generate seismic waves, or signals, which propagate into the geological formations and create pressure changes and vibrations along their way. Changes in elastic properties of the geological formations scatter the seismic waves, changing the waves' directions of propagation and other properties. Part of the energy that is emitted by the sources reaches seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the seismic sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposits.
Traditional seismic data processing is based on the premise that the seismic measurements are insufficient for purposes of resolving the thickness of a bedding layer, which is less than one quarter of the wavelength of the seismic signal. However, a hydrocarbon deposit may be contained in a relatively thin bedding layer that has a thickness that is less than the one quarter wavelength threshold. Examples of such thin bedding layers include sediment layers that are formed by streams, rivers, bay deposits, turbidic flows and the fragmented remains of talus slopes that are generated by wave action against reefs. Therefore, the one quarter wavelength limitation precludes the discrimination of relatively thin geological features and, in general, may prevent the discovery of certain oil and gas deposits.
Thus, there is a continuing need for better ways to process a seismic signal to detect an attribute (a thickness, for example) of a geological layer that has a thickness that is less than one quarter of the seismic signal's wavelength.